Dendrochronology

Dendrochronology (Greek, â€˜study of time by treesâ€™) is the use of tree rings to date past events which modified the structure of the tree rings. Trees lay down annual rings, the width of which in cross-section indicates the length and quality of the growing season when the wood was laid down. Thus the age of a tree can be determined by counting the total number of rings, and deductions can be made about climatic conditions during historical periods by the thickness of rings of known age. Certain trees can live for thousands of years and can therefore reveal information about climate in prehistoric times. Rings from different trees can be matched up so that the rings found in ancient timbers can be matched with rings in trees felled at a known date. This enables an absolute chronology of climatic changes to be determined, data which is of great use in archaeology. The term was coined by the founder of the science, the astronomer Andrew Douglass, who first investigated tree rings while looking for evidence of past sunspot cycles in vegetation. RB